Process for preparation of 1-benzylimidazole compound

ABSTRACT

Disclosed is a process for the preparation of a 1-benzylimidazole compound represented by the following general formula: ##STR1## wherein R 2  represents a lower alkyl group or phenyl group, and R 4  represents a hydrogen atom or a methyl group, 
     which comprises heating and to react a 1-unsubstituted imidazole compound represented by the following general formula: ##STR2## wherein R 2  and R 4  are as defined above, with benzyl alcohol in the presence of a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof or a lower alkyl ester thereof, and neutralizing the reaction product with an alkali.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a process for preparing a 1-benzylimidazole compound by benzylation of a 1-unsubstituted imidazole, and also to a novel 1-benzylimidazole compound. The 1-benzylimidazole compound is valuable as a curing agent and a curing promoter for a polyepoxy resin.

(2) Description of the Related Art

A process for reacting a 1-unsubstituted imidazole compound with benzyl chloride, cooperating with an HC acceptor in an appropriate solvent having no active hydrogen atom is known [see, for example, Recl. Trev. Chim. Pays-Bas, Vol. 91, No. 12, 1383-1392 (1972)].

This benzylation process, however, involves the following problems. Namely, the 1-imidazole compound formed by the reaction between the 1-unsubstituted imidazole compound and benzyl chloride is likely to react further with unreacted benzyl chloride to form a 1,3-dibenzyl imidazolium chloride compound, and therefore, the unnecessary imidazolium chloride is formed as a by-product in a large quantity. Moreover, benzyl chloride is difficult to handle because of the lacrimatory property.

SUMMARY OF THE INVENTION

Under this background, we made research with a view to solving the above-mentioned problems, and as a result, it was found that a 1-benzylimidazole compound can be obtained at a high efficiency by heating to react a 1-unsubstituted imidazole compound with benzyl alcohol in the presence of a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof or a lower alkyl ester thereof and neutralization of the reaction product with an alkali.

It was also found that a 1-benzylimidazole compound is similarly obtained by reactng a 1-unsubstituted imidazole compound with a benzyl ester of a carboxylic acid and neutralizing the reaction product with an alkali.

We have now completed the present invention based on these findings.

More specifically, in accordance with one aspect of the present invention, there is provided a process for the preparation of a 1-benzylimidazole compound represented by the following general formula: ##STR3## wherein R₂ represents a lower alkyl group or phenyl group, and R₄ represents a hydrogen atom or a methyl group,

which comprises heating and to react a 1-unsubstituted imidazole compound represented by the following general formula: ##STR4## wherein R₂ and R₄ are as defined above, with benzyl alcohol in the presence of a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof or a lower alkyl ester thereof, and neutralization of the reaction product with an alkali.

In accordance with another aspect of the present invention, there is provided a process for the preparation of a 1-benzylimidazole compound represented by the following general formula: ##STR5## wherein R₂ represents a lower alkyl group or a phenyl group, and R₄ represents a hydrogen atom or a methyl group,

which comprises heating to react a 1-unsubstituted imidazole compound represented by the following general formula ##STR6##

wherein R₂ and R₄ are as defined above, with a benzyl ester of a carboxylic acid and neutralization of the reaction product with an alkali.

DETAILED DESCRIPTION OF THE INVENTION

The preparation process of the present invention is represented by the following reaction formulae: ##STR7## wherein R₂ represents a lower alkyl group or a phenyl group, R₄ represents a hydrogen atom or a methyl group, and R represents a carboxylic acid residue.

In the reaction of formula I, the carboxylic acid, carboxylic anhydride or benzyl or lower alkyl ester thereof is used in an amount of 0.01 to 1.0 mole, preferably 0.05 to 0.4 mole, per mole of the imidazole compound. Benzyl alcohol is used in an amount of 1.05 to 1.5 moles per mole of the imidazole compound. The reaction temperature is 200° to 300° C., preferably 230° to 260° C. In this case, the reaction is completed within 4 hours. The reaction can be carried out under atmospheric pressure or under such a reduced pressure that benzyl alcohol is not distilled. Water formed by the reaction is removed from the reaction system in the form of an azeotrope (boiling point=98° C.) by distillation. In order to remove a small amount of water that remains in the reaction mixture, the pressure is reduced to about 600 mmHg at the state where the reaction is sufficiently advanced, or scavenging is carried out by using an inert gas.

In the reaction of the present invention, a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof and a lower alkyl ester thereof exert the catalytic action. This is a novel finding.

After an alkali hydroxide has been added to the reaction mixture in an amount sufficient to effect the neutralization, distillation is carried out under a reduced pressure, a crude intended 1-benzylimidazole compound can be obtained.

After an alkali hydroxide has been added to the crude compound in a molar quantity corresponding to the unreacted imidazole compound, distillation under a reduced pressure is carried out again, the intended compound substantially free of the unreacted imidazole compound can be obtained.

The carboxylic acid, the carboxylic anhydride and the benzyl ester thereof, are benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, isophthalic acid, terephthalic acid, succinic acid, maleic acid, adipic acid, and anhydrides and benzyl esters thereof (inclusive of semiesters of polycarboxylic acids).

The benzyl ester of the carboxylic acid is obtained by heating to react benzyl alcohol with a corresponding carboxylic anhydride or carboxylic acid. Accordingly, in carrying out the present invention, a carboxylic acid and benzyl alcohol can be used in combination instead of the carboxylic acid ester itself.

It is known that a lower alkyl ester of a carboxylic acid is easily ester-exchanged with benzyl alcohol to form a benzyl ester by heating (the low alkyl alcohol is distilled out of the reaction system because of its lower-boiling point).

Accordingly, a lower alkyl ester of a carboxylic acid, such as a methyl ester, an ethyl ester, a propyl ester, an isopropyl ester or a butyl ester can be used, in carrying out the present invention, respectively.

In the process represented by reaction formula [II], the benzyl ester of the carboxylic acid should be used in an amount equal to, or slightly larger than, the equivalent amount of the imidazole compound. The reaction temperature is generally 200° to 300° C. and preferably 230° to 260° C. In this case, the reaction is completed within 4 hours. After the carboxylic acid component of the reaction mixture has been neutralized with an alkali, an organic solvent (such as acetone) is added to the reaction mixture, and the mixture is filtered and the filtrate is subjected to distillation under a reduced pressure, whereby a crude intended 1benzylimidazole compound can be obtained. An alkali hydroxide is added to the crude intended compound in a molar quantity corresponding to the unreacted imidazole compound and distillation under a reduced pressure is carried out again, whereby an intended compound substantially free from the unreacted imidazole compound is obtained.

As the typical carboxylic acid used for the synthesis of the benzyl ester, there can be mentioned benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, isophthalic acid, terephthalic acid, maleic acid and adpic acid, and acid anhydrides thereof.

The benzyl ester (inclusive of a semiester) of the carboxylic acid can be obtained by heating benzyl alcohol with a corresponding carboxylic anhydride or carboxylic acid while distilling water formed by the reaction from the reaction system.

Typical imidazole compounds used in the present invention include 2-methylimidazole (hereinafter referred to as "2MZ"), 2-ethylimidazole (hereinafter referred to as "2RZ"), 2-isopropylimidazole (hereinafter referred to as "2IZ"), 2-phenylimidazole (hereinafter referred to as "2PZ"), 2-ethyl-4-methylimidazole (hereinafter referred to as "2E4MZ"), and 2-phenyl-4-methylimidazole (hereinafter referred to as "2P4MZ").

The properties of 1-benzylimidazoles prepared according to the process are described below. Incidentally, 1-benzyl-2-ethylimidazole, 1-benzyl-2-ethyl-4(5)-methylimidazole are novel compounds.

1-Benzyl-2-methylimidazole ##STR8##

Neutral colorless crystal having a melting point of 48° to 52° C. (hexane) and being hardly soluble in water but easily soluble in alcohols, acetone and benzene, TLC (silica gel, methanol, I₂ coloration):

Rf=0.60 to 0.75

IR: ^(KBr) _(cm) ⁻¹ 3400(19), 3030(23), 1675(30), 1610(35),

1590(37), 1530(29), 1500(24), 1475(26),

1455(24), 1430(22), 1360(28), 1290(25),

1205(47), 1160(32), 1135(30), 1080(38),

1035(33), 990(30), 932(47), 850(42),

730(21), 700(25), 680(29)

Each parenthesized value indicates the percent transmission.

1-Benzyl-2-ethylimidazole ##STR9##

Weakly basic colorless liquid having a boiling point (bp24) of 186° to 191° C. can being insoluble in water but easily soluble in alcohols, acetone and chloroform.

TLC(silica gel, acetone, I₂ coloration):

Rf=0.32 to 0.45

IR νliquid film 3110(44), 3070(45), 3040(42),

cm⁻¹ 2980(32), 2940(37), 2880(45),

1603(48), 1520(43), 1495(23),

1451(24), 1428(26), 1370(45),

1353(41), 1330(47), 1273(34),

1180(53), 1150(43), 1120(48),

1070(42), 1040(42), 1025(45),

960(54), 910(53), 832(55),

720(20), 688(33)

Each parenthesized value indicates the percent transmission.

NMR(CDCl₃): δ7.0-7.4, m, 5H; 6.98, S, 1H and 6.82

S, 1H; 5.04, S,2H; 2.63, q(J=7hz),

2H; 1.28, t(J=7Hz), 3H

Mass m/e: 186, 95, 91, 65

1-Benzyl02isopropylimidazole ##STR10##

Basic light-yellow liquid having a boiling point (bpl0) of 166° to 168° C. and being insoluble in water but easily soluble in alcohols, acetone and chloroform. TLC (silica gel, CHC₃ /MeOH=9/1, B.T.B. coloration):

RF =0.60 to 0.80

IR: νliquid film cm⁻¹ 3100(52), 3060(53), 3030(48),

cm⁻¹ 2960(37), 2920(41), 2860(47),

1600(59), 1510(53), 1480(39),

1450(39), 1350(45), 1270(41),

1162(51), 1145(51), 1060(42),

1010(55), 710(41), 680(44)

Each parenthesized value indicates the percent transmission.

NMR(CDCl₃): δ7.0-7.4, m, 5H(phenyl grup);

7.0, S, 1H and 6.8, S, 1H(4- and 5-positions);

5.1, S, 2H(methylene

group); 2.9, septet, 1H; 1.2, d, 6H

Mass m/e: 201(M⁺ +1), 200(M⁺), 185(M⁺ -CH₃),

157(M⁺ -isopropyl), 109(M⁺ -benzyl),

91(benzyl), 65

1-Benzyl-2-phenylimidazole ##STR11##

Neutral colorless crystal having a melting point of 51° to 53° C. (hexane) and being insoluble in water and hexane but easily soluble in alcohols, acetone and benzene.

TLC (silica gel, acetone, I₂ coloration):

RF=0.65 to 0.73

IR: νKBr 3100(38), 3055(35), 3025(36), 2920(40),

cm⁻¹ (1600(42), 1490(29), 1462(25), 1447(26),

1409(26), 1350(40), 1265(32), 1170(49),

1150(50), 1118(41), 1065(40), 1020*47),

1010(39), 990(51), 947(52), 903(46),

935(53), 760(28), 700(22), 682(16)

Each parenthesized value indicates the percent transmission.

NMR(CDCl₃): δ7.54, (J=6Hz), 2H(imidazole

ring); 7.4-6.9, m, 10H (phenyl); 5.21,

S, 2H(methylene)

Mass m/e: 235(M⁺ +1), 234(M⁺), 143, 91, 76, 65

1-Benzyl-2-ethyl04(5)-methylimidazole ##STR12##

Resin colorless crystal having a molting point of to 72° C. (toluene) and being insoluble in water but easily soluble in alcohols, acetone and chloroform. TLC (silica gel, methanol, I₂ coloration):

Rf=0.60 to 0.70

IR: νliquid film 3360(31), 3030(34), 2970(20),

cm⁻¹ 2930(22), 2870(35), 1950(65),

1810(65), 1650(58), 1600(53),

1570(50), 1493(25), 1450(18),

1420(19), 1378(44), 1350(40),

1320(47), 1295(34), 1160(51),

1065(38), 1025(46), 1005(54),

980(60), 795(57), 725(22),

690(24)

NMR(CDCl₃): δ7.35-7.28, m, 3H; 7.05 and 6.91, m,

2H (inclusive of isomers); 6.75 and

6.51, S, 1H (proton of imidazole ring,

inclusive of isomers);

5.01 and 5.00, S, 2H (methylene,

inclusive of isomers); 2.60, q, 2H

methylene of ethyl); 2.20 and 2.07,

S, 3H (inclusive of isomers); 1.25, t,

3H (terminal methyl)

Mass m/e: 201(M⁺ +1), 200(M⁺), 185(M⁺ -methyl),

171 (M⁺ -ethyl), 134, 109 (M⁺ -benzyl),

92, 91, 89, 76, 65, 51, 42, 40

1-Benzyl-2-phenyl-4(5)-methylimidazole ##STR13##

Neutral light-yellow crystal having a melting point of 62° to 64° C. (acetone) and being insoluble in water but easily soluble in alcohols, acetone and chloroform. TLC (silica gel, MeOH, I₂ coloration):

Rf=0.80 to 0.90

IR νliquid film 3660(50), 3380(28), 3070(23),

cm⁻¹ 3040(25), 2950(29), 2920(25),

1960(60), 1890(63), 1810(62),

1640(51), 1605(35), 1570(17),

1495(17), 1470( 9), 1450( 6),

1405( 6), 1355(20), 1300(29),

1250(51), 1160(30), 1073(31),

1021(26), 915(48), 840(59),

800(38), 765( 9), 725( 9),

705(10), 690( 4)

NMR(CDCl₃): δ7.56-7.46 and 7.40-7.23 and 7.10-7.00,

m, 10H; 6.64, S, 1H

(imidazole ring); 5.10, B, 2H

(methylene); 2.24, S, 3H (methyl)

Mass m/e: 249(M⁺ +1), 248(M⁺), 158, 157,

101, 91, 59, 58, 56, 55, 46, 45,

43, 41, 39, 31

The present invention will now be described in detail with reference to the following examples that by no means limit the scope of the invention. EXAMPLES 1 THROUGH 25

A predetermined amount of a carboxylic acid, a carboxylic anhydride or a lower alkyl ester of a carboxylic acid is mixed with 0.1 mole of a 1-unsubstituted imidazole and 0.11 mole of benzl alcohol, and heating reaction was carried out under predetermined conditions. Then, an alkali was added to the reaction mixture to effect neutralization and salting-out. The formed oil layer was separated and collected, and the extract was subjected to distillation under a reduced pressure singly or in the presence of NaOH to obtain a crude intended 1-benzylimidazole compound. The experimental conditions and obtained results are shown in Table 1.

Incidentally, runs where benzyl alcohol was first esterified with a carboxylic acid, a 1-unsubstituted imidazole compound was added to the reaction system and heating reaction was then carried out are indicated by "esterification precedent" in column "Remarks".

When each of the obtained crude intended compounds was examined by TLC (silica gel/acetone), it was found that each crude intended compound contained only a very small amount of the unreacted imidazole.

                                      TABLE 1                                      __________________________________________________________________________                                 Reaction                                           Example                     Temperature                                        No.  Imidazole                                                                             Carboxylic Acid                                                                           (mole)                                                                              (°C.)                                       __________________________________________________________________________      1   2EZ    trimellitic acid                                                                          (0.005)                                                                             250                                                 2   2EZ    trimellitic acid                                                                          (0.005)                                                                             250                                                 3   2EZ    trimellitic acid                                                                          (0.005)                                                                             250                                                 4   2EZ    trimellitic acid                                                                          (0.01)                                                                              250                                                 5   2EZ    trimellitic acid                                                                          (0.02)                                                                              250                                                 6   2EZ    trimellitic acid                                                                          (0.03)                                                                              250                                                 7   2EZ    trimellitic acid                                                                          (0.04)                                                                              250                                                 8   2EZ    trimellitic anhydride                                                                     (0.01)                                                                              250                                                 9   2EZ    phthalic acid                                                                             (0.03)                                                                              250                                                10   2EZ    phthalic anhydride                                                                        (0.01)                                                                              250                                                11   2EZ    isophthalic acid                                                                          (0.01)                                                                              250                                                12   2EZ    isophthalic acid                                                                          (0.03)                                                                              250                                                13   2EZ    terephthalic acid                                                                         (0.01)                                                                              230≈260                                    14   2EZ    pyromellitic acid                                                                         (0.03)                                                                              250                                                15   2EZ    benzoic acid                                                                              (0.03)                                                                              250                                                16   2EZ    succinic acid                                                                             (0.01)                                                                              250                                                17   2EZ    malic acid (0.03)                                                                              250                                                18   2EZ    adipic acid                                                                               (0.03)                                                                              250                                                19   2EZ    monomethyl phthalate                                                                      (0.01)                                                                              250                                                20   2MZ    trimellitic acid                                                                          (0.02)                                                                              250                                                21   2MZ    terephthalic acid                                                                         (0.03)                                                                              250                                                22   2IZ    phthalic anhydride                                                                        (0.01)                                                                              250                                                23   2E4MZ  phthalic anhydride                                                                        (0.01)                                                                              250                                                24   2PZ    phthalic anhydride                                                                        (0.01)                                                                              250                                                25   2P4MZ  trimellitic acid                                                                          (0.01)                                                                              250                                                __________________________________________________________________________     Example                                                                             Reaction                                                                              Post Treatment                                                                              Yield                                                 No.  Time(hours)                                                                           Conditions   (mole %)                                                                            Remarks                                          __________________________________________________________________________      1   4      NaOH 1.6 g, water 20 ml                                                                     76.3                                                   2   4      not neutralized                                                                             72.0                                                   3   4      in the presence of                                                                          84.0 esterification                                               NaOH 1.0 g        precedent                                         4   4      in the presence of                                                                          68.0                                                              NaOH 1.2 g                                                          5   4      NaOH 1.6 g, water 20 ml                                                                     76.3                                                   6   3.5    NH.sub.4 OH  74.7                                                   7   4      NaOH 1.6 g, water 30 ml                                                                     69.3                                                   8   4      in the presence of                                                                          65.0                                                              NaOH 1.6 g                                                          9   3      NH.sub.4 OH  87.6                                                  10   4      in the presence of                                                                          88.0                                                              NaOH 1.0 g                                                         11   10     in the presence of                                                                          76.9 esterification                                               NaOH 1.2 g        precedent                                        12   6      NH.sub.4 OH  76.0                                                  13   8      in the presence of                                                                          74.7                                                              NaOH 1.0 g                                                         14   3      NH.sub.4 OH  74.0                                                  15   4      NH.sub.4 OH  87.6                                                  16   4      in the presence of                                                                          74.0                                                              NaOH 1.0 g                                                         17   3.5    NH.sub.4 OH  71.0                                                  18   3      NH.sub.4 OH  55.0                                                  19   4      in the presence of                                                                          76.9                                                              NaOH 1.2 g                                                         20   3.5    NH.sub.4 OH  59.3                                                  21   5      NH.sub.4 OH  83.7                                                  22   4      in the presence of                                                                          84.0                                                              NaOH 0.8 g                                                         23   4.5    in the presence of                                                                          67.5 esterification                                               NaOH 1.0 g        precedent                                        24   5      in the presence of                                                                          81.0                                                              NaOH 1.0 g                                                         25   5      in the presence of                                                                          74.0                                                              NaOH 1.0 g                                                         __________________________________________________________________________

EXAMPLES 26 THROUGH 34

A benzyl ester of a carboxylic acid was added to 0.1 mole of a 1-unsubstituted imidazole compound in an amount equivalent to the amount of the imidazole compound (3.3 equivalents), and heating reaction was carried out under predetermined conditions and the reaction mixtue was subjected to neutralization and salting-out wih an alkali. The formed oil layer was separated and collected. Then, neutralization was carried out according to need, and the mixture was dried to the solid under a reduced pressure, extracted with methanol and subjected to distillation under a reduced pressure to obtain a crude intended 1-benzylimidazole compound. The experimental conditions and obtained results are shown in Table 2. When the crude intended compound was examined by the thin layer chromatography in the same manner as in the preceding examples, it was found that only a very small amount of the unreacted imidazole was contained as an impurity.

                                      TABLE 2                                      __________________________________________________________________________                         Reaction                                                                              Reaction                                            Example    Benzyl Ester of                                                                         Temperature                                                                           Time Yield                                          No.  Imidazole                                                                            Carboxylic Acid                                                                         (°C.)                                                                          (hours)                                                                             (mole %)                                                                            Remarks                                   __________________________________________________________________________     26   2EZ   monobenzyl                                                                              250    4    63   drying to solid and                                  phthalate                 extraction with metha-                                                         nol after neutralization                  27   2EZ   dibenzyl 250    2    50   drying to solid and                                  phthalate                 extraction with metha-                                                         nol after neutralization                  28   2EZ   dibenzyl 250    4    72   neutralization and                                   maleate                   salting-out                               29   2EZ   dibenzyl 250    4    78   neutralization and                                   adipate                   salting-out                               30   2MZ   benzyl   250    4    58   neutralization and                                   benzoate                  salting-out                               31   2MZ   dibenzyl 250    6    50   neutralization and                                   terephthalate             salting-out                               32   2MZ   dibenzyl 250    4    73   neutralization and                                   isophthalate              salting-out                               33   2IZ   tribenzyl                                                                               250    4    78   drying to solid and                                  trimellitate              extraction with metha-                                                         nol after neutralization                  34   2E4MZ dibenzyl 250    4    72   neutralization and                                   succinate                 salting-out                               __________________________________________________________________________

REFERENTIAL EXAMPLE 1

Curing performances of 1-benzylimidazole compounds to liquid polyepoxy resins were examined.

A predetermined amount of a 1-benzylimidazole compound obtained according to the present invention was added as a curing agent to 100 parts by weight of a polyepoxy resin (Epikote #828 supplied by Yuka-Shell Epoxy), and the composition was cast into a space of 3 mm between two glass sheets. The case composition was maintained at 100° C., and the temperature was elevated to 150° C. and heating was conducted for 4 hours to effect curing.

The storage stability and gel time of each composition and the properties of the cured product were examined. The obtained results are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________      ##STR14##                                                                                     ##STR15##                                                      __________________________________________________________________________     Amount (parts by weight)                                                                      10     3     5     10                                           Storage Stability*.sup.1                                                                      1.09   7.44  1.65  1.27                                         Gel Time       8'26"  2'18" 3'58" 2'36"                                        (hot plate method, 150° C.)                                             Glass Transition                                                                              147    131   119   131                                          Temperature                                                                    (TMA method, °C.)                                                       Linear Expansion                                                                              61 × 10.sup.-6                                                                  72 × 10.sup.-6                                                                 72 × 10.sup.-6                                                                 69 × 10.sup.-6                         Coefficient (deg.sup.-1, 25° C.)                                        Volume Resistivity                                                                            8 × 10.sup.15                                                                   2 × 10.sup.15                                                                  5 × 10.sup.15                                                                  2 × 10.sup.15                          (Ω · cm, 25° C.)                                         Dielectric Constant                                                                           2.93   3.04  3.71  3.23                                         (60Hz, 25° C.)                                                          Dielectric Loss (60Hz,                                                                        0.24   0.37  0.54  0.54                                         25° C., %)                                                              Flexural Strength                                                                             7.1    6.6   7.9   11.1                                         (Kgf/cm.sup.2, 25° C.)                                                  Flexural Modulus                                                                              361    290   332   297                                          (Kgf/cm.sup.2, 25° C.)                                                  Boiling Water Absorption                                                                      0.99   0.86  0.72  0.80                                         (8 hours' boiling, % by                                                        weight)                                                                        __________________________________________________________________________      Note                                                                           .sup.*1 ratio of viscosity of composition after standing for 24 hours at       25° C. to initial value of viscosity                              

REFERENTIAL EXAMPLE 2

Curing-promoting performances of 1-benzylimidazole compounds to acid anhydrides were examined.

A composition comprising 100 parts by weight of a polyepoxy resin (#Epikote #828 supplied by Yuka-Shell Epoxy), 87.4 parts by weight methyl-Δ⁴ -tetrahydrophthalic anhydride (Epichlon B570 supplied by Dai-Nippon Ink Kagaku Kogyo) and 0.5 part by weight of an imidazole compound was cast in a space of 3 mm between two glass sheets. The cast composition was maintained at 100° C. for 2 hours, and the temperature was elevated to 150° C. and the composition was heated for 4 hours to effect curing.

The storage stability and gel time of each composition and the properties of the cured product were examined. The obtained results are shown in Table 4.

The presence of a gelatinous substance (the salt of the acid anhydride with the imidazole) was not found in any composition.

                                      TABLE 4                                      __________________________________________________________________________      ##STR16##                                                                                     ##STR17##                                                      __________________________________________________________________________     Storage Stability.sup.*1                                                                      2.71   4.33  2.61  2.60                                         Gel Time.sup.*2                                                                               19'30" 17'24"                                                                               16'39"                                                                               18'18"                                       Glass Transition                                                                              126    129   120   122                                          Temperature (TMA method,                                                       °C.)                                                                    Linear Expansion Coeffi-                                                                      65 × 10.sup.-6                                                                  59 × 10.sup.-6                                                                 66 × 10.sup.-6                                                                 58 × 10.sup.-6                         cient (deg.sup.-1, 25° C.)                                              Volume Resistivity                                                                            2 × 10.sup.16                                                                   1 × 10.sup.16                                                                  4 × 10.sup.15                                                                  7 × 10.sup.15                          (Ω · cm, 25° C.)                                         Dielectric Constant                                                                           2.91   2.82  3.57  3.13                                         (60Hz, 25° C.)                                                          Dielectric Loss                                                                               0.53   0.58  0.84  0.74                                         (60Hz, 25° C., %)                                                       Flexural Strength                                                                             14.5   13.6  13.2  13.8                                         (Kgf/cm.sup.2, 25° C.)                                                  Flexural Modulus                                                                              349    318   327   371                                          (Kgf/cm.sup.2, 25° C.)                                                  Boiling Water Absorption                                                                      0.64   0.73  0.53  0.57                                         (4 hours' boiling, % by                                                        weight)                                                                        __________________________________________________________________________      Note                                                                           .sup.*1 ratio of viscosity after standing at 40° C. for 24 hours t      initial value of viscosity                                                     .sup.*2 time required for stopping of rotational viscometer when               composition was maintained at 120° C.                              

We claim:
 1. A process for the preparation of a 1-benzylimidazole compound represented by the following formula: ##STR18## wherein R₂ represents a lower alkyl group or phenyl group, and R₄ represents a hydrogen atom or a methyl group,which comprises heating a 1-unsubstituted imidazole compound represented by the following formula: ##STR19## wherein R₂ and R₄ are as defined above, with benzyl alcohol in the presence of a carboxylic acid, a carboxylic anhydride, a benzyl ester thereof or a lower alkyl ester thereof, and neutralizing the reaction product with an alkali.
 2. A process for the preparation of a 1-benzylimidazole compound represented by the following formula: ##STR20## wherein R₂ represents a lower alkyl group or a phenyl group, and R₄ represents a hydrogen atom or a methyl group,which comprises heating a 1-unsubstituted imidazole compound represented by the following formula: ##STR21## wherein R₂ and R₄ are as defined above, with a benzyl ester of a carboxylic acid and neutralizing the reaction product with an alkali.
 3. 1-Benzyl-2-ethylimidazole.
 4. A compound selected from the group consisting of 1-benzyl-2-ethyl-4-methylimidazole and 1-benzyl-2-ethyl-5-methylimidazole.
 5. A compound selected from the group consisting of 1-benzyl-2-phenyl-4-methylimidazole and 1-benzyl-2-ethyl-5-methylimidazole. 